A controversial Will Hopoate try, in which Tony Williams was bizarrely ruled to have accidentally knocked the ball on to himself in the lead-up, has helped Canterbury to a 34-16 NRL win over St George Illawarra.

Hopoate's try, that Williams put down to divine intervention and was quickly coined the `Hand of Dog' try, pushed the Bulldogs out to a 10-point lead after 60 minutes at ANZ Stadium on Monday before 20,153 fans, a lead they never relinquished.

Commentators, players and officials alike were bewildered at what happened in the lead up to Hopoate's try as Williams effectively passed the Steeden to himself as he approached the Dragons line, a move once made famous by Dally Messenger and long outlawed in the NRL.

Williams then passed off to Hopoate to score. Referee Jared Maxwell awarded a try before referring it to the bunker where the decision was upheld by review official Luke Patten.

"I think God helped me there, but play it as it is, we got the try," Williams told Triple M, in his first game back after a stint in reserve grade.

Maxwell explained the decision to an exasperated Dragons captain Gareth Widdop "there was no deliberate push forward, it's not a knock on unless it touches someone".

According to NRL rules, a player who knocks on deliberately will be penalised. But play is allowed to proceed if a a player accidentally knocks on and regathers, and that is the way the bunker ruled.

The try was a crucial turning point and broke much of the Dragons' spirit.

Kerrod Holland added a penalty goal soon after and when Josh Reynolds pounced on a dropped ball in the 70th minute to race away and score the game was over.

It was a deflating end to what had promised to be a closely-fought game throughout an entertaining first half.

Kurt Mann and Tyson Frizell scored tries for the Dragons. Sam Perrett, Michael Lichaa and Moses Mbye also crossed for first half four-pointers as the Dogs enjoyed a 16-12 lead at halftime.

Mann scored his second shortly after the break to tie the scores at 16-all.

Curtis Rona scored out wide off a lovely Will Hopoate pass in the 58th minute before Hopoate's unusual touchdown.

Williams' touch brought back memories of Diego Maradona's `Hand of God' moment at the 1986 FIFA World Cup and Manly's `Hand of Foran' in the NRL's final series several seasons ago.